1. Field of the Invention
The present invention relates to a storage silo for difficultly flowing bulk material, which is to be discharged at the bottom end of the silo and which is provided with deceleration baffles.
2. Brief Description of the Background of the Invention Including Prior Art
The discharging of difficultly flowing bulk material from a tower silo or a storage silo is rendered difficult by the formation of bridges and/or domes inside of the column of bulk material present in the silo, which bridges and domes interfere with the gravitation induced flow of the bulk material. Then the bulk material cannot move or cannot move fast enough to be discharged from the silo, since insufficient amounts of material continue to slide to the lower silo end. The bulk material cannot be sufficiently gripped and taken by the mechanical devices in general disposed at the bottom end of a silo such as for example worms, scraping devices, agitators, stirrers, slideways and the like.
A silo of the kind initially set forth is known from the German Patent Laid Open No. 1,951,754. The frictional deceleration device of this silo comprises several wedges, which in a plan view on the silo form three groups disposed at a distance behind each other, which in each case take up a central angle of less than 120 degrees. The wedges are staggered within each group with increasing distance from the bottom, where at the same level of the silo in each case are provided three wedges, each of which belonging to another of the three groups. At this arrangement of the baffles special measures are necessary to avoid a clamping and/or bridging of the silo bulk material between the wedges neighboring in circumferential direction. The inclined side faces provided for this purpose at the wedges are in fact effective with many difficultly flowing materials, however, under difficult conditions they are not always in a position to prevent the formation of bridges. A further silo with a frictinal deceleration device is known from German Patent Application Laid Open De-OS No. 2,318,560, which comprises several conical baffles, which are disposed at a distance on top of each other at the silo wall and which are adjoining the silo walls with their upper edges. The decelerating surface of these baffles also runs inclined from the silo wall to the silo bottom. These baffles increase the frictional values between bulk material and silo wall, whereby a predetermined weight part of the bulk material column is accepted by the silo wall. The thereby reduced vertical loads effect in the respective planes of the bulk material column a reduction of the horizontal tensions, which exert an important influence on the stability of bridges and domes within bulk material columns.
The angle of inclination of the conical baffles has to be selected such that it does surpass the specific angle of repose of the bulk material in each case in order to prevent the motion of the bulk material upon discharge to come to an end. Then no such horizontal tension can arise within the column of bulk material, which would lead to the build-up of stable bridges and domes. Thus in the dimensioning of these baffles the kind of the bulk material to be stored or respectively its angle of repose have to be taken into consideratin. With many bulk materials the critical horizontal tensions can be disposed below a certain value, which tensions would lead above the certain critical value depending on the kind of the bulk material in the column to the formation of rigid and stable bridges and domes in these known silos. The stability and rigidity of the bulk mateial are then too low for the formation of supporting bridges and domes, and under these conditions bridges or domes collapse continuously. Silos comprising the described frictional deceleration devices have proven to be of value in the context of small, medium and large volume silos for numerous difficulty flowing bulk mateials, such as for example wood chips, dust, sludge, chemical and mineral materials, and root chips.
In case materials with a particularly high bulk density are to be stored in such silos, which materials in addition can be compressed to a large degree such as for example peelings and bark, in particular pine bark, then particular difficulties arise at the discharging of the materials stored. The unloading of a bulk material column comprising such fibrous materials cannot be metered such that a substantially constant relationship is achieved between the wall friction and the residual load of the column of bulk material. Depending on the structural state in each case of the bulk material there is also a constant change for the ratio between the decelerating effect and the residual load of the column. Thereby the decelerating friction frequently becomes too low such that the vertical load and the horizontal tensions caused therewith prevail. At a changed state of the structure the decelerating friction can be too large such that the motion of the column of bulk material stops at one or more places, since the residual load is insufficient to keep the gravitation induced flow going of the bulk material. In the two cases despite different causes the same effect occurs: the bulk material cannot be discharged any longer. The reason for this phenomenon is based on the described behavior of the bulk material, which can be compared to some extent with the behavior of rubber.